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A chemical reaction in ancient Roman concrete makes it stronger over time (2017)
- uniformlyrandom 7y ago1. Only in salt water 2. Only over time 3. And actually we still do not know. Slightly disappointing.
- mysterypie 7y ago> We may think we're at the height of human knowledge, but the ancients did possess precious knowledge that has been lost to time. I would love to hear why a chemical analysis doesn't solve the riddle here. Scientists were able to isolate a strain of the coronavirus and publish the entire genetic sequence in a matter of days, but we can't analyze a sample of concrete?
- BiteCode_dev 7y agoAvailable resources for the tasks are probably different.
- deleted 7y ago[deleted]
- cmroanirgo 7y agoJust as carbon ash from the fireplace has the same chemical makeup as a diamond, there's a bit more to it: namely the changing structure of the stuff itself. The CSH reaction (https://en.wikipedia.org/wiki/Calcium_silicate_hydrate https://en.wikipedia.org/wiki/Calcium_silicate_hydrate) is something that evolves over time, and even then the modern chemical reaction is not completely known in all its states (as far as I'm aware). > The [balanced chemical mass] of C-S-H in cement paste is variable and the state of chemically and physically bound water in its structure is not transparent, which is why "-" is used between C, S, and H The article actually misses how modern concrete (portland) get stronger over the first few years as the crystalline structures grow. So, I can well understand how it's a bit tricky to find out what the original roman mix was, just using observations 2000 years later: because a lot of things have happened from the original cake mix to what we see now.
- catalogia 7y ago> Just as carbon ash from the fireplace has the same chemical makeup as a diamond AFAIK wood ash is predominantly mineral oxides, particularly of calcium. The carbon in the wood is the fuel that burns up and goes out the chimney as carbon dioxide. When wood burns it first boils and burns off various volatile compounds, leaving behind black charcoal coals, made predominately of carbon. This charcoal also burns, leaving behind wood ash.
- kragen 7y agoI think they meant charcoal.
- blihp 7y agoYou can chemically analyze a piece of cake and know exactly what it's made of. You would still not know how to make one with that knowledge alone.
- rnestler 7y agoI guess some chemical reactions which happen over time are kind of like hash functions. So it's hard the find out what the input was just by observing the output.
- b0rsuk 7y agoI'm not a chemist, but perhaps a good analogy is making Mona Lisa with Game of Life? Recently posted on HN. Finding Mona Lisa in the Game of Life https://news.ycombinator.com/item?id=22552006 https://news.ycombinator.com/item?id=22552006 From the article: "This looks kinda cool, but what if we want to find a Life state that eventually, after following the rules of Life for a few rounds, reaches a state that looks like Mona Lisa? This requires working backwards instead of forwards from the target picture, which is a much more difficult problem. (...) We call Life state A the "parent" of state B if A turns into B by following the rules of Life. The reason that it's difficult to find the parent of a state is that the rules of Life are non-reversible. There's no direct way to go from a Life state to its parent, and in fact, it's possible for a state to have multiple parents or even no parents. "
- lazyjones 7y agoI'm sure they can analyze a sample of 2000 years old concrete, but it's not going to look the same as when it was built and it'll probably not be a simple mix of basic elements but very complex. The Romans might have used a mixture with actual lava or corals e.g. and it'd be hard to trace it back to such ingredients.
- 29athrowaway 7y agoAnother interesting piece of lost ancient knowledge: https://en.wikipedia.org/wiki/Greek_fire https://en.wikipedia.org/wiki/Greek_fire
- eb0la 7y agoAnother lost product, though you can find modern recreations in amazon: https://en.m.wikipedia.org/wiki/Damascus_steel https://en.m.wikipedia.org/wiki/Damascus_steel
- deleted 7y ago[deleted]
- dguest 7y agoWe might not use that any more, but unfortunately the concept of lighting one's enemy on fire hasn't gone away. What about flamethrowers? Napalm? Is there any indication that Greek fire is somehow more destructive than the modern shop of incendiary horrors?
- jstimpfle 7y agoRelated video that I liked: https://www.youtube.com/watch?v=pW-SOdj4Kkk https://www.youtube.com/watch?v=pW-SOdj4Kkk
- trappist 7y agoIs this subject to survivorship bias? Will future generations wonder at the inexplicable durability of a few modern structures still available to wonder at, for accidental reasons?
- exclusiv 7y agoNo. We make shit these days. Fast and cheap. 20 yrs is a long time.
- loeg 7y agoWe tend to build bridges out of steel nowadays for all kinds of reasons (cost, speed, durability, strength), and steel ain't gonna last 1000 years. There's not a lot of benefit to designing for 1000 year endurance.
- icanhackit 7y agoI considered that as well. I live in an area of town where a lot of 110+ year old town houses still stand proudly (European cities would laugh at that statement) but I know that only the stuff built well is standing today while whatever had been made to a lower quality crumbled and was built over. Just because old buildings survive to this day doesn't mean everything from that era was built to last. With regards to the featured article, I'd say multiple factors are at play - Roman concrete has amazing properties and structures that used it combined with good quality-control (i.e. correct material ratios in the concrete) and good engineering survived. The human elements, quality-control and design, are less interesting than a magical substance.
- antiterra 7y agoSome prior discussion on this at https://news.ycombinator.com/item?id=20482050 https://news.ycombinator.com/item?id=20482050 The top comment there links to two other discussions.
- lazylizard 7y agoI had this impression that pozzolans were a thing... Like. Solved problem.
- jonplackett 7y agoThis is amazing - I wonder if some luck was involved. I’m sure they were deliberately trying to make strong/lasting concrete but they couldn’t have tested it over hundreds of years, let alone 1000s. Is there a degree of chance to it being this effective?
- pietroglyph 7y agoThis seems like it's a great example of survivorship bias: the Romans probably made lots of concrete that didn't survive the elements, but there was some that the Romans did get lucky with. It's also possible that we don't see a similar thing today because our manufacturing processes are so much more standardized (and critically, they are standardized around a process that is apparently less robust.)
- londons_explore 7y agoThere are literally thousands of types of concrete you can buy today, and even now occasionally you get a 'bad batch' that doesn't test as strong as it's supposed to be. That indicates there must be quite a bit of per batch variation too. Overall, considering we build far more things per day than the Romans did, I reckon there's a good chance more of our buildings are around in 2000 years than the Romans have left now
- jaclaz 7y agoThe point is not much about strength (and measured strength according to norms) but rather about durability and strength over time. With "modern" cement (Portland) it is relatively easy to get high strength at 4 weeks/28 days, while (good ol') pozzolanic cement the reaction/hardening is much slower but over time (and with adequate humidity) it can reach and beat the "better" portland cement. Almost nothing we build today will be there in 2000 years, but not because of the concrete itself, but because of the reinforcing steel we use (and because of the different use of concrete in much slimmer structures). Anecdata: in the '80's/'90's I was working in a large tunnel project and we used in tunnels pozzolanic cement (not reinforced) for the lower part of the lining, and it was not easy to get the "right" (according to norms) 28 days strength (250 Kg/cm^2 at the time), but, once the tunnel was finished (roughly 3-5 years laters) and we did further testing of the structures, we found that it reached strength of the order of magnitude of 500-600 Kg/cm^2 whilst the corresponding Portland based concrete, targeted at the same 250 Kg/cm^2, reached "only" 300-350 Kg/cm^2.
- allovernow 7y agoOur modern building practices and materials are not optimized for longevity. What incentive in modern times does a contractor have in building homes that last hundreds of years? The average person is too ignorant to know or care anyway.
- totalZero 7y agoThe average person doesn't build his home in seawater.
- loeg 7y agoRoman concrete is slow setting and didn't have rebar. We prefer to build quickly (more efficient use of land multiplied by time) and prefer our buildings not fall over in earthquakes. Also much of residential construction is wood frame (edit: US), which also has pretty bad longevity unless extremely overbuilt.
- chrisseaton 7y ago> much of residential construction is wood frame Why is this?
- hobofan 7y agoIt's cheaper.
- jsilence 7y agoWhishing people would realize it is also much more sustainable.
- chrisseaton 7y agoEven if you have to rebuild every 50 years or so? A brick structure will last thousands of years.
- pitdicker 7y agoIt is always a bit annoying to read an article based on the work of someone specialized in one area that talks down specialists in another area. Is is definitely interesting to read about some unexpected properties that ancient concrete with volcanic ash as one of its ingredients has. For modern cement there is a different set of choices for binding materials, were you can choose the ingredients that are locally good available. Also there are definitely mistakes that get made in modern construction. - Maybe the structure has enough rebar to handle the forces that act on the structure, but not enough to prevent the small cracks that hurt durability (although that is something that should be checked). - Maybe the detailing of the rebar is not correct. Lapping lengths are too short. Often I see that the workers who put in the rebar come up with creative solutions but understanding why it now doesn't work well is outside their expertise. - Maybe the concrete layer that protects the rebar (covering) from rusting is to thin or to porous. The amount of covering required depends on the exposure classification. And the concrete mixture influrences how porous the concrete becomes over the years. For modern engineering you specify the exposure classes that a structure falls in. Carbonatation (https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation), a reaction where calcium in the concrete with CO2 in the air, which changes the acidity in the concrete. Chlorids, from sources such as seawater or de-icing salts, also impact the acidity of the concrete. Chemical acids, basically everything biological such as milk, beer, manure, and other acids dissolve the calcium. And frost can cause parts of the concrete to flak off. All those effects can get worse if the concrete gets porous. But all are well understood problems that inform the necessary mixture.
- jf___ 7y agoA material science professor at TU Delft [1] and this material is commercially available [2]. From the abstract of `Bacteria-Based Self-Healing Cementitious Composite for Application in Low-Temperature Marine Environments` [3]: "The composite displayed an excellent crack-healing capacity, reducing the permeability of cracks 0.4 mm wide by 95%, and cracks 0.6 mm wide by 93% following 56 days of submersion in artificial seawater at 8 ◦C. Healing of the cracks was attributed to autogenous precipitation, autonomous bead swelling, magnesium-based mineral precipitation, and bacteria-induced calcium-based mineral precipitation in and on the surface of the bacteria-based beads. " [1] https://www.tudelft.nl/citg/over-faculteit/afdelingen/materials-mechanics-management-design-3md/sections-labs/materials-environment/staff/dr-hm-henk-jonkers/ https://www.tudelft.nl/citg/over-faculteit/afdelingen/materi... [2] https://www.basiliskconcrete.com/hoe-werkt-het/?lang=en https://www.basiliskconcrete.com/hoe-werkt-het/?lang=en [3] doi:10.3390/biomimetics2030013
- dang 7y agoRoman concrete threads may not be made of Roman concrete, but they do ok: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&query=roman%20concrete&sort=byDate&type=story https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que... Last year: https://news.ycombinator.com/item?id=20482050 https://news.ycombinator.com/item?id=20482050 2017: https://news.ycombinator.com/item?id=14690329 https://news.ycombinator.com/item?id=14690329 2013: https://news.ycombinator.com/item?id=5883443 https://news.ycombinator.com/item?id=5883443 2010: https://news.ycombinator.com/item?id=1852000 https://news.ycombinator.com/item?id=1852000
- dghughes 7y agoI'm more amazed at how long of a period ~1,000 years where people forgot about concrete.
- __initbrian__ 7y agoAll concrete gets stronger over time! https://www.concrete.org/tools/frequentlyaskedquestions.aspx?faqid=13 https://www.concrete.org/tools/frequentlyaskedquestions.aspx... edit: [adding more detail, removing all caps] Contracts will often specify a 7day or 28day strength because the concrete will keep getting stronger over time. Separate cylinders are poured for independent testing of the strength Here’s a good textbook on concrete: Concrete: Microstructure, Properties, and Materials Textbook by Paulo J. M. Monteiro and Povindar Kumar Mehta